1. Field of the Invention
The present invention relates to an imaging apparatus and a method for control the imaging apparatus, and more particularly relates to an imaging apparatus including a mechanical shutter and a control method for the same.
2. Description of the Related Art
As discussed in Japanese Utility Model Publication No. 6-26895, a direct-holding type focal-plane shutter holds first and second curtains of a shutter in a charge state by energizing electromagnets corresponding to the first and second curtains and controls an exposure time by successively stopping energizing respective electromagnets.
As discussed in Japanese Patent Application Laid-Open No. 2005-283897, there is a direct-holding type focal-plane shutter that can reduce electric power consumption by changing a power voltage during energization control for the electromagnets.
Furthermore, as discussed in Japanese Patent Application Laid-Open No. 58-149027, an electromagnetically-driven shutter includes a temperature detector that measures the temperature of a shutter blade driving coil and a reference voltage generation circuit that generates a corrected reference voltage according to a temperature change in the shutter blade driving coil. The exposure time is appropriately controlled based on the corrected reference voltage.
Furthermore, as discussed in Japanese Patent Application Laid-Open No. 2001-215555 and Japanese Patent Application Laid-Open No. 2001-23220, there is a conventional camera including an image sensor (e.g., a charge coupled device (CCD) sensor or a complementary metal-oxide semiconductor (CMOS) sensor) that enables a user to view an object displayed on a monitor (e.g., liquid crystal display (LCD)) in a state where a first curtain opens an aperture of the shutter while a second curtain is continuously held. This function is generally referred to as “electronic viewfinder (EVF)”, and an image displayed via the EVF is referred to as “live view.”
However, if the focal-plane shutter discussed in Japanese Utility Model Publication No. 6-26895 is incorporated in an imaging apparatus having an EVF discussed in Japanese Patent Application Laid-Open No. 2001-215555 or Japanese Patent Application Laid-Open No. 2001-23220, the following problems arise.
A monitor display, when executed, requires continuously energizing the electromagnet that holds the second curtain. Therefore, not only electric power consumption increases but also the departure timing of the electromagnet changes due to heat generation in the electromagnet. Thus, the accuracy in exposure control deteriorates. Furthermore, for a similar reason, the accuracy in exposure control deteriorates in a bulb shooting operation, which requires a long time exposure.
The electric power consumption and heat generation in the electromagnet can be reduced if the focal-plane shutter discussed in Japanese Patent Application Laid-Open No. 2005-283897 is used. However, the cost increases because a dedicated circuit is required to switch the voltage applied to the electromagnet. Furthermore, the departure timing of the electromagnet changes if the electromagnet generates heat regardless of power voltage control.
Furthermore, the electromagnetically-driven shutter discussed in Japanese Patent Application Laid-Open No. 58-149027 can stabilize the accuracy in exposure control based on a voltage correction, considering heat generation in the coil, by detecting the temperature of the shutter blade driving coil.
However, the above-described electromagnetically-driven shutter requires a dedicated temperature detector and a circuit that can correct the control voltage. Accordingly, the cost increases. Furthermore, the time available for switching the voltage is short and insufficient if the shutter operates in a high-speed shooting operation. Thus, actual application of the technique discussed in Japanese Patent Application Laid-Open No. 58-149027 is substantially limited to a low-speed shooting operation.